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Agree with Witek. Broken sleeve of center duct actuator can cause non stop clicking and motor noise. Notch of the sleeve is what stops the motor. You need to check the flap inside the duct just like the user on the above link. If the flap is constantly turning, diagnosis is correct and the fix is easy. SDS resetting is not a must. Here are the pictures of the broken sleeve and location of the motor (after removal).

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